This invention relates generally to catheters and particularly to coronary dilatation catheters for use in administering treatments to widen a constricted blood flow passage in, for example, a heart valve or a coronary artery.
A stenosis is a region of a blood vessel which has been narrowed to such a degree that blood flow is restricted. If the stenosis is sufficiently severe, treatment is required to restore adequate blood flow. Often such treatment requires surgery or angioplasty. Percutaneous transluminal coronary angioplasty is a procedure for treating a patient having a stenosis or constricted region in a coronary artery. In some patients it is possible to expand a stenosis so that the artery will permit an acceptable blood flow rate.
Coronary angioplasty comprises the insertion of a balloon catheter through the patient's left femoral artery and heart into the arterial stenosis and injecting a suitable fluid into the balloon to expand the stenosis radially outward, compressing the stenosis against the arterial wall. Therefore, angioplasty has become an alternative to coronary arterial bypass surgery for many patients. If the stenosis is comprised primarily of fatty deposits, rather than an appreciable amount of calcium, and if the stenosis is not too severe, it is often possible to compress the stenosis radially outward against the adjacent arterial wall to increase the cross sectional area of the artery so that the artery has an acceptable blood flow rate therethrough.
Ordinary balloon catheters have a balloon fastened around the exterior of a hollow catheter tube. A thin line fastened to the balloon and the exterior surface of the catheter provides means for connecting the balloon to a suitable fluid supply for inflating the balloon. The hollow catheter tube provides means for injecting fluids into the artery for diagnostic and therapeutic purposes.
Prior coronary dilatation catheters used in coronary angioplasty have the disadvantage of completely occluding blood flow while the balloon is expanded in the artery. Any complete occlusal of a coronary artery cannot be permitted for more than about ten seconds without incurring serious risk of damage to the portions of the heart which should receive blood from the occluded artery. Therefore, the balloon may be pressurized for only a few seconds before the balloon must be allowed to depressurize for permitting resumption of blood flow through the region of the stenosis.
The problem of occluding blood flow is particularly acute in patients having a left main coronary artery lesion. Ordinary catheters even without balloons may cause spasm by narrowing the left main coronary artery, which supplies blood to a large portion of the heart.
A cardiologist administering an angioplasty treatment ordinarily does not know exactly how much pressure to apply to the balloon to achieve satisfactory results. Excessive pressure in the balloon may dissect the artery, which may cause serious damage to the patient's heart. Therefore, the cardiologist positions the balloon in the artery, expands the balloon, allows the balloon to depressurize and removes the catheter from the artery to permit measurement of the blood flow rate past the stenosis. If the blood flow rate is not acceptable, then the cardiologist repeats the angioplasty treatment until the blood flow rate is acceptable or until the cardiologist determines that angioplasty will be unable to restore the blood flow rate to an acceptable value.
It is possible that the mere presence of an ordinary balloon catheter into the stenosis for more than ten seconds will seriously occlude blood flow and cause a risk of heart damage. It is also possible for a patient's artery to experience a complete occlusal or blockage after the balloon catheter is withdrawn from the artery. Rapid restoration of blood flow is necessary to prevent heart damage if any artery completely occludes.
Performing a coronary angioplasty involves the additional difficulty of inserting the balloon catheter into the desired coronary artery. Most balloon catheters are too flexible for direct insertion into a patient's coronary arteries; and accordingly a guide catheter or a guide wire guides the balloon catheter to the proper position in the artery designated for treatment. A cardiologist first inserts the guide catheter or guide wire into the ostium of the artery selected for treatment and then inserts the balloon catheter through the guide catheter to position the balloon across the stenosis. Catheters are generally characterized as being either selective or unselective. Unselective guide catheters ordinarily permit insertion only into the aorta. Various types of selective catheters permit insertion into the left and right main coronary arteries, but are unable to provide reliable means for inserting a balloon into the coronary arteries branching from the main coronary arteries. The catheter sometimes hangs against an arterial wall near an arterial ostium causing trauma, which leads to spasm. Even selective catheters may require a few hours of trial and error for insertion into a coronary artery in some cases, and in some patients, it is impossible to insert a selective catheter into the artery designated to receive the angioplasty treatment without the risk of excessive trauma and spasm in the arteries leading to the stenosis.
Percutaneous balloon valvuloplasty may be an alternative to open heart surgery for certain patients having congenital pulmonary valve stenosis. The catheter and deflated balloon are advanced through the femoral vein and heart to the pulmonary artery and across the stenotic valve. A cardiologist uses a manually operated pumping device to inflate the balloon for four or five seconds at a time.
The balloon contains a radiopaque dye, which permits visual monitoring of the process. Blood flow is occluded through the pulmonary artery during the inflation period, which must, therefore, be as short as possible in order to avoid systemic hypotension and bradycardia. The balloon catheter is withdrawn after the force of the inflated balloon ruptures the valve.
About one of every 1,500 children is born with pulmonary valve stenosis. If the condition is left untreated, the strain of pumping blood through the narrowed pulmonary valve causes excessive pressure in the right ventricle, leading to possible heart failure. Surgical correction of pulmonary valve stenosis requires about ten days of hospitalization, leaves a surgical scar, carries a relatively greater risk of morbidity and mortality and is very expensive. In contrast, balloon valvuloplasty ordinarily requires approximately three days of hospitalization, has a very low morbidity and mortality risk, is performed under local anaesthesia, which is safer than the general anaesthetic required for open-heart surgery and costs about one-third as much as open-heart surgery. Still, however, the necessity of deflating the balloon every four or five seconds is a great inconvenience encountered in the use of prior balloon catheters.